The present invention relates to an improved door controller for roller type doors.
Such doors are well known and comprise a flexible door curtain which can be raised and lowered from a drum located above the door aperture. It is also well known to employ a pair of end drums rotatably mounted on a fixed axle extending horizontally across the top of the door aperture. The curtain is secured at its upper end to each of the spaced end drums and a ring gear is secured to one drum and provided with a motor drive for rotating the drums and thereby raising or lowering the door.
Door controllers of the type having a remote control transmitter which sends a coded signal to a controller coupled to the door drive means for controlling raising and lowering the door are also well known. These controllers usually operate in conjunction with mechanically operated upper and lower limit switches and obstruction detection devices. The forms of obstruction detection are many and include mechanical sensors in the lower portion of the door curtain, motor load monitoring devices, and run time monitors.
Each of these systems has inherent disadvantages and particular problems have been found with the type of door described above where the downward movement of the door is dependent upon the weight of the door curtain causing the door curtain to fall into the door opening. In such doors the changes in motor load will be dependent on the position of the door. Furthermore, the relationship between motor load and door position will vary with door age, climatic conditions and track condition. Thus setting of load monitoring device to only detect actual obstructions is difficult as each of these variations must be compensated for in order to avoid false tripping of the door mechanism.